Peristaltic pump

ABSTRACT

A peristaltic pump in which the material and thickness of the wall of the tube are chosen so that, at a predetermined pressure differential, between the exterior and interior, collapse of the tube wall to a flattened condition occurs, thereby causing restriction in the flow rate of liquid in the tube as a function of the pump inlet pressure.

United States Patent 1191 Sausse Jan. 8, 1974 [54] PERISTALTlC PUMP 2,572,658 10/1951 Perkins 251/5 x [75] Inventor: Andre Sausse, Sceaux, France [73] Assignee: Phone-Poulenc S.A., Paris, France Primary Examiner-Carlton Cmyle Assistant Examiner-Richard E. Gluck [22] Ffled: 1972 Attorney-W. Warren Taltavull [21] Appl. No.: 304,975

Related US. Application Data [63] Continuation of Ser. No. 83,305, Oct. 23, 1970, [5 ABSTRACT abandoned.

A peristaltic pump in which the material and thickness [52] US. Cl. 417/53, 417/477 of the wall f the tube are ehgsen so that at a predei F04b F04b /0 termined pressure differential, between the exterior Field of Search 417/477, 476, 475, and interior, collapse Qf the tube wall to a flattened 251/5 condition occurs, thereby causing restriction in the flow rate of liquid in the tube as a function of the [56] References Cited pump inlet pressure.

UNITED STATES PATENTS 3,180,272 4/1965 Broadfoot 417/475 X 2 Claims, 8 Drawing Figures PATENTED 8W4 3, 784.323

sum 2 OF 4 i A 0 U15 Audza mlnvenlor A Home y PATENTEI] JAN 81974 SHEET Q [If 4 1 PERISTALTIC PUMP This is a continuation, of application Ser. No. 83,305, filed Oct. 23, 1970 now abandoned.

BACKGROUND OF THE INVENTION The present invention relates to a peristaltic pump, which maybe used, for example, for transferring blood from a patient to an extra-corporal circulation device.

It is known that peristaltic pumps are suitable for extra-corporal circulation devices because of their simplicity of operation and because they avoid any contact of the blood with frictional surfaces responsible for various hazards. However, they suffer from a serious disadvantage inherent in all volumetric pumps; their flow rate is a function of their speed.

If such a pump is connected to a vein and driven by a constant speed motor, it sucks the blood at a practically constant rate whilst the vein is supplied at an unknown rate, which depends particularly on the position of the body, on the arterial pressure and on the average venous pressure. If the supply of the vein drops below the flow rate of the pump, the vein is gradually emptied of its blood and collapses. In the extreme case the puncture needle can cause lesion of the wall of the vessel.

Regulating devices have been proposed which either control the speed of the pump by the pressure reduction created upstream or by the level of the blood in a tank interposed between the patient and the pump. These devices are delicate and bulky and have not found general application.

According to the present invention there is provided a peristaltic pump comprising at least one flexible compressible tube, means for successively compressing the pumping portion of said tube at two points spaced apart and moving the points of compression longitudinally along said portion. The tube, at least along said pumping portion, has such a wall thickness and is made of such a material that collapse of the walls of the pumping portion will occur when a predetermined pressure differential exists between the interior and exterior of the pumping portion to restrict the volume aspired therein.

Preferably the predetermined pressure differential between the interior and the exterior of the pumping portion is less than 250 cms of water. A suitable material for the collapsible portion of the tube is a silicone elastromer. The wall thickness of the collapsible portion may be any suitable value, for example less than 2 millimetres.

With the pump according to the invention should the pressure in the tube fall below the predetermined value, the tube will begin to collapse or flatten and thus restrict the volume of liquid aspired therein.

In order that the invention may more readily be understood, the following description is given merely by way of example, reference being made to the accompanying drawings in which;

FIG. 1 shows one embodiment of pump according to the invention, interposed between a patient and a haemodialyser; 1

FIG. 2 is a graph showing how the cross-section of the tube changes as a function of the differences in pressure;

FIG. 3 is a graph schematically showing the relationship between the shape and the surface of the crosssection of the tube;

FIGS. 4 and 5 are graphs showing the operating curves of a pump according to the invention as a function of various parameters;

FIGS. 6a, 6b, and show sectional elevation of embodiments of a roller of the pump flattening the tube.

The pump 10 illustrated in FIG. 1 as shown is used for pumping blood from the arm 11 of a patient to a dialyser 12 and back to the arm. An upstream portion 13 of flexible tubing is connected to a pumping portion 14, which, in turn, is connected to a downstream portion 15 leading to the dialyser. The pumping peristaltic action is produced by three rollers 16 having larger diameter portions at their longitudinal centers than at their ends. The three rollers 16 are rotatable as a set about a central axis 17 and the rollers are also rotatable about their own axes. Secured to a support 18 are two clamps 19 and 20 which are arranged to tension the pumping portion 14 over the array of rollers 16. Thus, the pumping portion is lightly stretched and the downstream portion 13 and the upstream portion 15 of the tube are below the pumping portion 14.

In the most general case used, the pump mayfunction in open air, and the differences in pressure arise solely from the variations in the internal pressure of the tube. However, the possibility of placing the pump inside a controllable pressure chamber is not excluded, and in this case the differences in pressure arise either from the variations in the pressure of the chamber alone or, simultaneously, from the variations in the chamber pressure and the internal pressure of the tube.

Again in the most general case, the pressure inside the upstream portion of the tube is lower than the external pressure and the tube in its relaxed position is cylindrical. Under, these conditions,there is a range of pressure differences (called the sensitive range) in which the free (or internal) cross-section of the tube changes gradually from a circle to a flatter and flatter ellipse. FIG. 3 shows how the surface S of an ellipse of constant circumference varies as a function of the length of itssmall axis A. Thelimit S lOO and A 1 corresponds to the circle. The free cross-section of a tube approximately obeys this law but departs therefrom in the caseof substantial flattenings: the tube then assumes the characteristicsliape bf aii or ofa Emits bell, and two smaller passages are left on either side of a central portion where the walls touch. The residual passages are very much less sensitive to pressure than the initial tube, and the broken line has been used to show how the free cross-section of the tube varies in reality in this region of maximum flattening. I

1 The tube can also be manufactured to have an elliptical or fusiform cross-section when relaxed. In thiscase,

the free cross-section can vary both under the effect of an internal reductionin pressure and of an internal excess pressure.

In both of these cases the variations in the free crosssection are due to a flexing of the walls of the tube.

The free cross-section can also vary through elastic stretching of the wall, with the tube increasing in diameter under the action of the internal pressure. Such an expansion however demands much higher differences in pressure and does not occur in the case of flexible but inextensible tubes. Hence pumps in which the tubes change in cross-section through flexing of the wall are preferred; this allows a considerable variation in flow rate for a small variation in pressure, contrary to what would be the case with a change in cross-section by stretching.

It is obvious that the flattening of the tube must be gradual and that the pressure/flattening curve for the change occurring in either direction must display neither any zero slope nor any splitting into two (due to hysteresis or doubly stable positions); this would amount to having two different cross-sections, and hence two different flow rates, for one and the same pressure, which is obviously incompatible with a control system.

The sensitive range of these tubes varies as a function of well-known parameters (internal diameter, wall thickness and modulus of elasticity), and it is hence easy to determine what tube is suitable for a particular application, either by empirical tests or by calculation. It is possible to standardize a series of tubes once and for all by measuring their flattening for different suction pressures; FIG. 2 shows the standardisation of three silicone elastomer tubes of internal/external diameters 9/l2, lO/l2.6 and 12/14 mm. The ordinate of the graph indicates the thickness of the tube (small external axis) and the abscissa shows the internal pressure reduction, expressed as the height of water raised, all in mm. The forking of the curve corresponds to the appearance of an 8-shaped cross-section with the opposite walls of the tube touching in the middle part (this is not a case of the characteristic displacement of a hysteresis).

Knowing the average flow rate required of the pump, it is easy to choose a suitable cross-section of tube as a function of mechanical characteristics of the pump for example, (pulsation frequency, and distance between two nip points,) i.e., volume per pulse. Thus the tube itself is chosen as a function of the sensitive range, or visa versa. FIG. 4 shows how the maximum flow rate of a pump varies for a given speed of rotation as a function of the pressure reduction in the suction tube and the lifting pressure, expressed in centimetres of water. For a given speed and a given delivery pressure, it is thus possible to vary the average flow rate by simply changing the height of the pump, so that the peristaltic tube falls in the central portion of the sensitive range.

The internal pressure of the peristaltic tube at the pump inlet is equal to the sum of three pressures:

a. the pressure of the liquid to be pumped (measured at the point of withdrawal);

b. the height between the pump and the liquid to be pumped; and

c. the loss in pressure upstream from the pump (especially at the fixed or adjustable throttling point such as a puncture needle, clip or tap.)

If the internal pressure lies within the sensitive range, i.e., so that the pressure differential between the interior and exterior is sufficient to cause collapsing of the tube, any variation in pressure of the liquid to be pumped manifests itself through a variation in pressure in the peristaltic tube, causing a variation in its crosssection and its flow rate. Thus the flow rate necessary and sufficient to maintain a quasi-constant pressure upstream from the pump is self-regulating.

This regulation is not absolute (as in any servomechanism) but suffices in themajority of cases. It is however useful to recall that the loss in pressure upstream from the pump, for a given liquid andagiven pipeline,

varies as a function of the flow rate; the regulation of the flow rate is hence the better, when its variations and the loss in pressure are smaller.

The pumps according to the invention are particularly suitable for use as level regulators, because a rise or lowering of the level of the liquid to be pumped respectively causes an increase or reduction in the flow rate of the pump. They are equally suitable for the extra-corporal circulation of blood (for example for haemodialysis), and very particularly when the circulation is from a vein supplied by an arterio-venous fistula; it is, in effect, known that the average pressure in the vein, at the point of entry of the withdrawal needle, can vary. When this pressure drops, the flow rate of a pump according to the invention decreases spontaneously. Thus emptying the vein to the point of complete flattening, which would cause the hazards indicated above, is avoided.

Furthermore, in the event of an utimely movement of the patient, the end of the intravenous needle or catheter can come close to the wall of the vessel and change the pressure drop of the whole device. Under these conditions, if the flow rate does not drop very rapidly, the end of the needle or catheter can adhere by suction to the wall of the vessel, entirely stop the flow and cause lesion of the wall.

Although the mechanical part of the pump can theoretically be of any type (with fingers, with rollers and a fixed idling stator or without stator), a rotating pump without stator is preferred in practice. Amongst the pump os this type, a pump with 3 rollers, such as is shown in FIG. 1, is preferred. This pump in effect has particularly valuable advantages in cases where the life of a patient is at stake because if the delivery tube should be partially or completely clocked it acts as a pressure restrictor. (In this case the liguid can flow back through the elastic tube which is blocked only through its tension around at least one roller, instead of being flattened between two incompressible elements, and the pump feeds more or less nothing and thus does not present the risk of causing the tube to burst.)

Although the pump functions correctly in any position, it is advantageous to locate the pumping tube in a non-horizontal (preferably vertical) plane, with its pumping portion, as illustrated in FIG. 1, at a higher level than its outlet section; this arrangement allows a bubble of air accidentally introduced into the circuit to be retained if the speed of the. liquid pumped is less than the speed of rise of the bubble. This is the case particularly for haemodialysis, where the blood flow rate is low (6.5 to 7 cm/sec in a tube of about one centimetre diameter).

According to an advantageous characteristic, especially in the case of a blood pump, the pumping tube is not entirely blocked at the point of the pressure elements, fingers or rollers (at least for the position of the rotor which corresponds to the minimum elongation of the tube in normal operation in the case of a pump without stator): the tube remains open along a crosssection of between 0.01 and 2 mm and preferably about 1 mm. Under these conditions the back-flow of blood upstream is negligible but the backflow of air is complete; the pump cannot feed air towards the patient. When the pump has built up sufficient air it stops and requires the removal of air from the pump to restart.

To avoid complete blockage of the tube of a pump with rollers and a stator, it suffices to leave a space greater than the thickness of a completely flattened tube between these elements. A similar adjustment is appropriate for a pump with fingers. In the case of a pump with rollers and without a stator, it suffices to vary the tension of the tube. The latter will be determined by the following parameters of the pump: speed of rotation, flow rate, delivery pressure, relative thickness and elastic characteristics of the tube, and diameter of the rollers. Determining this presents no difficulty; for example, it is sufficient gradually tor-change the tension until the desired result is obtained.

Preferably the rollers are not cylindrical but have a smaller diameter at the point of the lateral folds of the tube than in their middle portion. They can, in particular, be a double cone or a doubly conically tapered cylinder. This shape facilitates adjusting the tension of the tube (as defined above) and improves the risistance of the tube to repeated flexing. This shape is also suitable for pumps with a stator, in particular to avoid complete blockage of the tube.

A pump without a stator equipped with a stretched tube has an additional advantage; its maximum delivery pressure can be defined with a small margin of variation over a large part ofits range of flow rates (see FIG. 4 and Example 2)..

The tube with which a pump according to the invention is equipped can be made of any elastic material sufficiently resistant to repeated flexing, and expecially of elastomers which are suitable for customary peristaltic pumps. Silicone elastomers generally prove satisfactory for biological liquids and furthermore their elastic memory is excellent. Additionally, a tube according to the invention has a thinner wall than in the customary pumps because it must flex as a function of the variations in internal pressure. This reduction in thickness improves the working life of the tube, which is an additional advantage, especially in the case of extracorporal circulation.

The peristaltic pump according to the invention possesses the advantages of centrifugal pumps (variable flow rate at constant speed) without suffering from their disadvantages (settling-out and destruction of shaped elements), nor from those of volumetric pumps. It thus simultaneously provides optimum guarantees of safety in suction, in delivery and with regard to the accidental indroduction of air into its suction.

The Examples which follow illustrate various aspects of the invention:

EXAMPLE 1 For circulating the blood of patients fitted with arterio-venous fistulas and treated by chronic haemodialysis, the pump represented in FIG. [has the following characteristics: I

Doubly conical rollers, diameter 6 mm at the centre, apex angle 430, spaced at 120 from one another on a circle of 60 mm radius,

silicone elastomer tube of diameter 9 X 12 mm, hardness 55 Shore, stretching by percent under the tension of a weight of 1.2 kg, I

Telaxedleiigth s5s''mm", length in operation 3 93 to 404 mm (depending on the angular position of the rollers). The pump sucks the blood through a puncture needle (internal diameter 1.6 mm) and lifts it into a haemodialyser connected by appropriate tubes. The

blood returns to the blood vessel by means of an identical needle.

In practice, a speed of about 25 rpm is chosen, corresponding to 75 pulsations; for an approximate height of 70 cm below the patient, and with average flattening of the tube, the blood flow rate is about 300 em /minute.

EXAMPLE 2 The following modifications are introduced intgthe pump of Example 1: rollers comprising a cylindrical middle part (12 mm length, 5 mm diameter) ending in truncated cones (length 5 mm, apex angle 430). These rollers, made of stainless steel, run with spindles carried in self-lubricated rings.

The tube has diameters of 10 and 12.6 mm, its relaxed length is 380 mm, and its minimum tension is 400 g. FIG. 4 represents the maximum flow rate curves of the pump as a function of the lift height (downstream pressure) for two suction heights (upstream presure reduction): 0 to 50 mm of mercury at 25 rpm. It is seen that for a suction of 50 mm Hg., the maximum flow rate only changes from 350 to 300 em /minute for a lift pressure of 0 to 220 mm Hg, whilst it drops from 300 to 0 between about 220 and 260 mm Hg. Safety against excessive delivery pressure is hence very rapidly ensured. The drop in flow rate between 0 and 220 mm Hg, is due to the intentional lack of leakproofnes's of the pump; its effect is hence small in the range of pressures used. In normal operation (speed 25 rpm, lift up to 120 mm Hg), the flow rates are 340 cm/minute for an upstream pressure reduction of 50 mm Hg and 410 cm /minute for zero pressure reduction.

FIG. 5 respectively shows:

At A, the maximum delivery pressure (mm Hg) as a function of the tension of the tube (in grams) at 25 rpm. The degrees of stretching of the tube for two tension extremes have been shown;

At B, the maximum delivery pressure as a function of the speed of the pump (in rpm) for a tube under 400 g. tension.

I claim:

1. A method of peristaltic pumping comprising providing a flexible compressible tube said tube being constructed from a silicone elastomer and a pumping portion thereof and reducing the inlet pressure to said tube until the pressure difference between the inside and outside of the pumping portion of the tube becomes so high that said pumping portion partially collapses along the entire length thereof, and successively compressing said partially collapsed pumping portion at spaced apart points of compression and moving the points of compression longitudinally of said portion thereby to reduce the available pumping volume whereby the output from the pump is controlled as a function of the inlet pressure.

2. A method of operating a peristaltic pump to pump liquid from a source, said pump being of the type comprising a flexible compressible tube, a pumping portion to said tube and means for successively compressing said pumping portion at spaced apart points of compression and moving the points of compression longitudinally of said portion, including the step of progressively increasing the height of the pump above the source of liquid to be pumped until said pumping portion at least partially collapses clue to reduction of the pressure of fluid within the tube thereby toreduce the available pumping volume whereby the output from the pump is controlled as a function of the inlet pressure. l

UNITED STATES PATENT OFFICE CERTIFICATE CORRECTION 3,784,323 I v Dated January 8 1224 Patent No.

Inventor (5). Andre sausse lt is cert i f ie'd that error appears and that said Letters Patent are hereby corrected as shown below:

"In the heading please insext:

October 27, 196Q.

Change the Assignee's name to read as follows:

hw-Pf uleno, S-

Sig n" ed and sealed this; 16th day ofJulyt 197 A Attest: McCOY r 1. GIBSON, JR. (1. MARSHALL DANN Attestlng Offioer Y Commissioner of Patents in the abo ve identified patent --Cle=imspriority, application France" No. 69 36805 Form PO-IOSO (10-69) 

1. A method of peristaltic pumping comprising providing a flexible compressible tube said tube being constructed from a silicone elastomer and a pumping portion thereof and reducing the inlet pressure to said tube until the pressure difference between the inside and outside of the pumping portion of the tube becomes so high that said pumping portion partially collapses along the entire length thereof, and successively compressing said partially collapsed pumping portion at spaced apart points of compression and moving the points of compression longitudinally of said portion thereby to reduce the available pumping volume whereby the output from the pump is controlled as a function of the inlet pressure.
 2. A method of operating a peristaltic pump to pump liquid from a source, said pump being of the type comprising a flexible compressible tube, a pumping portion to said tube and means for successively compressing said pumping portion at spaced apart points of compression and moving the points of compression longitudinally of said portion, including the step of progressively increasing the height of the pump above the source of liquid to be pumped until said pumping portion at least partially collapses due to reduction of the pressure of fluid within the tube thereby to reduce the available pumping volume whereby the output from the pump is controlled as a function of the inlet pressure. 